Prepare the watermelon by cutting it into manageable chunks, removing any seeds if needed, and chilling in the fridge or freezer for extra coolness.
Add the chilled watermelon chunks into a blender along with the ice cubes and lemon juice if using.
Secure the lid and blend on high speed, pulsing if necessary, until the mixture is smooth and frosty, resembling a slushy cloud.
Pause the blender to check the consistency; if it's too thick, add a splash of water or more lemon juice and blend again until creamy.
Pour the thick, icy watermelon mixture into glasses, watching it ooze in and settle into a vibrant pink swirl.
Serve immediately with a straw or spoon, enjoying the cool, refreshing texture and bright flavor of summer in a glass.
